From: Duncan Murdoch <murdoch.duncan_at_gmail.com>

Date: Fri, 27 Jan 2012 13:37:45 -0500

> Section 6.3 of IEEE 754-2008 says

> Except that squareRoot(−0) shall be −0, every numeric squareRoot result

*> shall have a positive sign.
*

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Fri 27 Jan 2012 - 18:44:09 GMT

Date: Fri, 27 Jan 2012 13:37:45 -0500

On 27/01/2012 1:26 PM, Duncan Murdoch wrote:

> On 27/01/2012 12:32 PM, Prof Brian Ripley wrote:

*> > On 27/01/2012 13:26, Duncan Murdoch wrote:
**> > > On 12-01-27 7:23 AM, Hans W Borchers wrote:
**> > >> I have a question concerning the new Windows toolchain for R>= 2.14.2.
**> > >> When trying out my package 'pracma' on the win-builder development
**> > >> version
**> > >> it will stop with the following error message:
**> > >>
**> > >> > f3<- function(x, y) sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1))
**> > >> > dblquad(f3, -1, 1, -1, 1) # 2.094395124 , i.e. 2/3*pi , err = 2e-8
**> > >> Warning in sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1)) : NaNs produced
**> > >> Warning in sqrt((1 - (x^2 + y^2)) * (x^2 + y^2<= 1)) : NaNs produced
**> > >> Error in integrate(function(y) f(x, y), ya, yb, subdivisions = subdivs, :
**> > >> non-finite function value
**> > >> Calls: dblquad ...
**> > >> <Anonymous> -> f -> do.call -> mapply -> <Anonymous> -> integrate
**> > >> Execution halted
**> > >> ** running examples for arch 'x64' ... ERROR
**> > >> Running examples in 'pracma-Ex.R' failed
**> > >>
**> > >> This probably means that the following expression got negative for some
**> > >> values x, y:
**> > >>
**> > >> (1 - (x^2 + y^2)) * (x^2 + y^2<= 1)
**> > >
**> > > I think you're right, it's a bug, hopefully easy to fix. Here's a
**> > > simpler version:
**> > >
**> > > x<- 0*(-1)
**> > > sqrt(x)
**> > >
**> > > x is a "negative zero", and the sqrt() function incorrectly produces a
**> > > NaN in the new toolchain.
**> >
**> > Well, for some definition of 'incorrectly'. It is clearly what the
**> > author of that piece of code intended.
**> >
**> > It would be helpful if people would cite definitive references. Someone
**> > is going to have to report this on the bugtracker, and at present I
**> > don't have enough evidence to do so: the C99/C11 standards do not seem
**> > to mandate a particular value (they do say what happens for values less
**> > than zero, but C compilers are allowed to have or not have signed
**> > zeroes). (Various Unix-alikes say what they do, usually -0, but that's
**> > not evidence that other answers are 'incorrect'.)
*

>

> Section 6.3 of IEEE 754-2008 says

>

> Except that squareRoot(−0) shall be −0, every numeric squareRoot result

I believe the corresponding ISO standard is ISO/IEC/IEEE 60559:2011, but I don't have a copy, and I don't think my library does.

Duncan Murdoch

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